Aquatic sediment pre extraction preparations and the effects on aroclor 1248 concentrations

Although there is extensive information regarding analysis of polychlorinated biphenyls (PCBs) in sediments, a standardized procedure for preparation of stream sediments prior to extractions has not been clearly established. Objectives of this study were to determine effects of wet versus dry sediment extractions on final PCB concentrations and to evaluate PCB relationships with sediment organic carbon (OC) and sediment particle size. Sediment samples were collected from the Mud River in southwestern Kentucky and analyzed by gas chromatography. Comparative treatments included wet samples; air-dried unsieved samples; and sieved samples, including gravel-coarse sa nd, medium sand, fine sand, and clay-silt fractions. Results among treatments did not differ significantly, but, compared with dry sediment assays, Aroclor 1248 concentrations were lower by 52-83% when wet sediments were extracted and expressed on a dry weight basis. Aroclor 1248 values also did not differ significantly among the four sieved sediments fractions, and no distinct trend was observed. Concentrations of Aroclor 1248 and sediment OC in the gravel-coarse sand fraction were greater than expected. Aroclor 1248 dry weight concentrations (mg/kg) correlated with sediment OC when the ratio of Aroclor 1248 to sediment OC was less than 1:10000. Results support basing final determination of PCBs on assays of dried and sieved sediments.